Method for manufacturing high silicon steel sheets



Patented May 29, 1951 METHOD FOR MANUFACTURING HIGH SILICON STEEL SHEETS William F. Nagel, Pittsburgh, Pa., assignor to United States Steel Company, a corporation of New Jersey No Drawing. Application March 3, 1949, serial No. 79,517

2 Claims.

This invention relates to improved methods for manufacturing high silicon steel sheets.

For the purpose of describing and claiming the present invention, I define the term high silicon steel as meaning steel which has the following composition by Weight:

Silicon, 3 to 6 percent Carbon, 0.02 to 0.15 percent Aluminum, 0.00 to 1.00 percent Manganese, 0.10 to 0.60 percent Phosphorous, 0.02 maximum Sulfur. 0.02 maximum and the balance iron and incidental impurities. Also I define the term sheets as including continuous lengths of the material in coil form, as well as cut lengths.

The improvements of the present invention are applicable to processes for manufacturing high silicon steel sheets in which ingots of such steel first are hot rolled into semi-finished shapes, such as slabs, blooms, or billets, and subsequently these shapes are hot rolled into sheets. Sometimes there is a considerable delay between the step of rolling the semi-finished shapes and the step of rolling the latter into sheets. It becomes necessary to cool the semi-finished shapes from their finishing temperature, which is in excess of 1500 F., and later to re-heat them to a temperature suitable for further hot rolling. In previous practices with which I am familiar, rolling the re-heated shapes has produced serious cracking in the steel and has necessitated excessive scrapping.

An object of the present invention is to provide improved methods for eliminating cracking in high silicon steels when semi-finished shapes of such steels are cooled and subsequently are re-heated and hot rolled.

A further object of the invention is to provide improved processes for manufacturing high silicon steels in which semi-finished shapes are cooled from their finishing temperature at controlled critical rates that enable them to be reheated and hot rolled without cracking.

When the present invention is practiced, high silicon steel ingots first are hot rolled into semifinished shapes, such as slabs, blooms or billets, by any conventional procedure. Their finishing temperature at this stage is in excess of 1500 F.

Preferably these semi-finished shapes would be hot rolled immediately into sheets without any intermediate cooling, but this is not always possible and it becomes necessary to cool and re-heat the shapes before they are rolled further.

According to the present invention, the semifinished shapes are cooled from their finishing temperature to a temperature between 1000 F. and 1100 F. at a critical maximum rate of 30 F. per hour or preferably to a temperature of about 1000 F. at a rate of 15 to 25 F. per hour. Then these shapes are cooled to a temperature between 600 and 800 F. at a critical maximum rate of 70 F. per hour or preferably to a temperature of about 700 F. at a rate of to F. per hour. The cooling rate below the latter temperature range does not appear to be critical to practicing the present invention.

The cooling rate of the semi-finished shapes can be controlled by any conventional apparatus and procedure. For example, immediately after the shapes are rolled and while they are still at their finishing temperature, which is in excess of 1500 F., they can be assembled into lifts or piles and placed in a pit furnace which has been preheated to this finishing temperature. The furnace is then cooled at a controlled rate so that its temperature decreases at a maximum rate of 30 F. per hour until it reaches 1000 F. to 1100 F. The rate of temperature decrease then can be changed to a maximum rate of F. per hour until the temperature reaches 600 F. to 800 F. The shapes then can be removed from the furnace pit and piled outside, where cooling can be completed to atmospheric temperature. Inasmuch as furnaces and temperature control means which are capable of furnishing controlled cooling rates are well known, no detailed disclosure of such apparatus is deemed necessary for an understanding of the present invention.

After the semi-finished shapes have been cooled in accordance with the present invention, they can be re-heated any time later to a hot rolling temperature and hot rolled further according to any conventional procedure. Such rolling does not crack the steel, and thus the present invention overcomes this dilficulty of previous practices with which I am familiar.

While I have shown and described only a single exemplary method of practicing the invention, it is apparent that variations may arise. Therefore, I do not wish to be limited to the disclosure as set forth but only by the scope of the appended claims.

I claim:

1. A process for manufacturing high silicon steel sheets having a silicon content of 3 to 6 percent comprising hot rolling ingots of such steel into semi-finished shapes at a finishing temperature in excess of 1500 F., cooling said semifinished shapes at a controlled maximum rate of 30 F. per hour until they reach a temperature of 1000 to 1100 F., cooling said semi-finished shapes further at a controlled maximum rate of 70 F. per hour until they reach a temperature of 600 to 800 F., cooling said semi-finished shapes further to atmospheric temperature, re-heating said semi-finished shapes to hot rolling temperatures, and hot rolling these shapes into sheets without cracking them.

2. A process for manufacturing high silicon steel sheets having a silicon content of 3 to 6 percent comprising hot rolling ingots of such steel intosemi-finished shapes at a finishing temperature in excess of 1500 F., cooling said semi-finished shapes at a controlled rate of 15 to 25 F. per hour until they reach a temperature 4 of about 1000" F., cooling said semi-finished shapes further at a controlled rate of 55 to 65 F. per hour until they reach a temperature of about 700 F., cooling said semi-finished shapes further to atmospheric temperature, re-heating said semi-finished shapes to hot rolling temperatures, and hot rolling these shapes into sheets without cracking them.

WILLIAM F. NAGEL.

REFERENCES CITED UNITED STATES PATENTS Name Date Corson Apr. 5, 1932 Number 

1. A PROCESS FOR MANUFACTURING HIGH SILICON STEEL SHEETS HAVING A SILICON CONTENT OF 3 TO 6 PERCENT COMPRISING HOT ROLLING INGOTS OF SUCH STEEL INTO SEMI-FINISHED SHAPES AT A FINISHING TEMPERATURE IN EXCESS OF 1500* F., COOLING SAID SEMIFINISHED SHAPES AT A CONTROLLED MAXIMUM RATE OF 30* F. PER HOUR UNTIL THEY REACH A TEMPERATURE OF 1000* TO 1100* F., COOLING SAID SEMI-FINISHED SHAPES FURTHER AT A CONTROLLED MAXIMUM RATE OF 70* F. PER HOUR UNTIL THEY REACH A TEMPERATURES OF 600* TO 800* F., COOLING SAID SEMI-FINISHED SHAPES FURTHER TO ATMOSPHERIC TEMPERATURE, RE-HEATING SAID SEMI-FINISHED SHAPES TO HOT ROLLING TEMPERATURES, AND HOT ROLLING THESE SHAPES INTO SHEETS WITHOUT CRACKING THEM. 